Microbicidal composition

ABSTRACT

A synergistic microbicidal composition having two components. The first component is a nonionic surfactant with structure: R 1 O(CH 2 CH(CH 3 )O) 5 (CH 2 CH 2 O) 9 H, where R 1  is a C 8  alkyl group. The second component is 2-methyl-4-isothiazolin-3-one. The weight ratio of the nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.005 to 1:1.3714.

This invention relates to microbicidal compositions containing 2-methyl-4-isothiazolin-3-one and a surfactant.

A composition containing 5-chloro-2-methylisothiazolin-3-one, 2-methylisothiazolin-3-one and a nonionic dispersant is disclosed in U.S. Pat. No. 4,295,932. The composition contains a 3:1 mixture of 5-chloro-2-methylisothiazolin-3-one and 2-methylisothiazolin-3-one, and a copolymer of ethylene oxide and propylene oxide which appears to have the same composition as PLURONIC L61 or TERGITOL L61 dispersant. However, there is a need for combinations of microbicides having synergistic activity against various strains of microorganisms to provide effective control of the microorganisms. Moreover, there is a need for such combinations containing lower levels of individual microbicides for environmental and economic benefit. The problem addressed by this invention is to provide such synergistic combinations of microbicides.

STATEMENT OF THE INVENTION

The present invention is directed to a synergistic microbicidal composition comprising: (a) a nonionic surfactant with structure:

R¹O(CH₂CH(CH₃)O)₅(CH₂CH₂O)₉H

where R¹ is a C₈ alkyl group; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.005 to 1:1.3714.

The present invention is further directed to a synergistic microbicidal composition comprising: (a) a nonionic surfactant with structure:

R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H

where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.006 to 1:0.9143.

The present invention is further directed to a synergistic microbicidal composition comprising: (a) a nonionic surfactant with structure:

R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₅H

where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.001 to 1:0.1143.

The present invention is further directed to methods for inhibiting the growth of microorganisms in aqueous media by adding to an aqueous medium a nonionic surfactant as described herein and 2-methyl-4-isothiazolin-3-one in the ratios described herein.

DETAILED DESCRIPTION OF THE INVENTION

“MIT” is 2-methyl-4-isothiazolin-3-one. As used herein, the following terms have the designated definitions, unless the context clearly indicates otherwise. The term “microbicide” refers to a compound capable of inhibiting the growth of or controlling the growth of microorganisms; microbicides include bactericides, fungicides and algaecides. The term “microorganism” includes, for example, fungi (such as yeast and mold), bacteria and algae. The following abbreviations are used throughout the specification: ppm=parts per million by weight (weight/weight), mL=milliliter. Unless otherwise specified, temperatures are in degrees centigrade (° C.), references to percentages are percentages by weight (wt %) and amounts and ratios are on an active ingredient basis, i.e., total weight of MIT and the nonionic surfactant. Numbers of polymerized units of propylene oxide or ethylene oxide are number averages.

Preferably, the weight ratio of the nonionic surfactant with structure:

R¹O(CH₂CH(CH₃)O)₅(CH₂CH₂O)₉H

where R¹ is a C₈ alkyl group to 2-methyl-4-isothiazolin-3-one is from 1:0.02 to 1:0.0571 or 1:0.12 to 1:1.3714. Preferably, the weight ratio of the nonionic surfactant with structure:

R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H

where R² is a mixture of C₈-C₁₄ linear alkyl groups to 2-methyl-4-isothiazolin-3-one is from 1:0.012 to 1:0.9143.

The present invention is further directed to a method for inhibiting the growth of mold, preferably A. niger, in an aqueous medium by adding: (a) a nonionic surfactant with structure:

R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H

where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.04 to 1:0.9143.

The present invention is further directed to a method for inhibiting the growth of mold, preferably A. niger, in an aqueous medium by adding: (a) a nonionic surfactant with structure:

R¹O(CH₂CH(CH₃)O)₅(CH₂CH₂O)₉H

where R¹ is a C₈ alkyl group; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.015 to 1:1.3714; preferably from 1:0.12 to 1:1.3714.

The present invention is further directed to a method for inhibiting the growth of yeast, preferably C. albicans, in an aqueous medium by adding: (a) a nonionic surfactant with structure:

R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H

where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.006 to 1:0.4571, preferably from 1:0.012 to 1:0.4571.

The present invention is further directed to an aqueous composition comprising from 15 to 40 wt % of 2-methyl-4-isothiazolin-3-one and a nonionic surfactant with structure:

R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₅H

where R² is a mixture of C₈-C₁₄ linear alkyl groups, wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.2 to 1:1. Preferably the composition comprises from 20 to 35 wt % of 2-methyl-4-isothiazolin-3-one, preferably from 20 to 30 wt %, preferably about 25 wt %. Preferably, the composition comprises from 5 to 70 wt % water, preferably from 10 to 70 wt %, preferably from 20 to 60 wt %, preferably from 40 to 60 wt %.

R² is a mixture of C₈-C₁₄ linear alkyl groups. Preferably, the C₈-C₁₄ linear alkyl groups comprise from 50 to 85 wt % C₈-C₁₀ linear alkyl groups and 15 to 50 wt % C₁₂-C₁₄ linear alkyl groups, preferably from 60 to 75 wt % C₈-C₁₀ linear alkyl groups and 25 to 40 wt % C₁₂-C₁₄ linear alkyl groups, preferably about 70 wt % C₈-C₁₀ linear alkyl groups and about 30 wt % C₁₂-C₁₄ linear alkyl groups. Preferably, the linear alkyl groups are derived from seed oil. Preferably, R¹ is 2-ethylhexyl.

Preferably, each of the compositions is substantially free of 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), i.e., it has less than 1 wt % of CMIT based on total weight of active ingredients, preferably less than 0.5 wt %, preferably less than 0.2 wt %, preferably less than 0.1 wt %. Preferably, each of the compositions is substantially free of microbicides other than the nonionic surfactant and MIT, i.e., it has less than 1 wt % of microbicides other than the nonionic surfactant and MIT based on total weight of active ingredients, preferably less than 0.5 wt %, preferably less than 0.2 wt %, preferably less than 0.1 wt %. Preferably, when the nonionic surfactant and MIT are added to an aqueous medium, the medium is substantially free of other microbicides, i.e., it has less than 1 wt % of microbicides other than the nonionic surfactant and MIT based on total weight of active ingredients, preferably less than 0.5 wt %, preferably less than 0.2 wt %, preferably less than 0.1 wt %.

The compositions of this invention may contain other ingredients, e.g., defoamers and emulsifiers. The microbicidal compositions of the present invention can be used to inhibit the growth of microorganisms or higher forms of aquatic life (such as protozoans, invertebrates, bryozoans, dinoflagellates, crustaceans, mollusks, etc) by introducing a microbicidally effective amount of the compositions into an aqueous medium subject to microbial attack. Suitable aqueous media are found in, for example: industrial process water; electrocoat deposition systems; cooling towers; air washers; gas scrubbers; mineral slurries; wastewater treatment; ornamental fountains; reverse osmosis filtration; ultrafiltration; ballast water; evaporative condensers; heat exchangers; pulp and paper processing fluids and additives; starch; plastics; emulsions; dispersions; paints; latices; coatings, such as varnishes; construction products, such as mastics, caulks, and sealants; construction adhesives, such as ceramic adhesives, carpet backing adhesives, and laminating adhesives; industrial or consumer adhesives; photographic chemicals; printing fluids; household products, such as bathroom and kitchen cleaners; cosmetics; toiletries; shampoos; soaps; personal care products such as wipes, lotions, sunscreen, conditioners, creams, and other leave-on applications; detergents; industrial cleaners; floor polishes; laundry rinse water; metalworking fluids; conveyor lubricants; hydraulic fluids; leather and leather products; textiles; textile products; wood and wood products, such as plywood, chipboard, flakeboard, laminated beams, oriented strandboard, hardboard, and particleboard; petroleum processing fluids; fuel; oilfield fluids, such as injection water, fracture fluids, and drilling muds; agriculture adjuvant preservation; surfactant preservation; medical devices; diagnostic reagent preservation; food preservation, such as plastic or paper food wrap; food, beverage, and industrial process pasteurizers; toilet bowls; recreational water; pools; and spas.

The specific amount of the microbicidal compositions of this invention necessary to inhibit or control the growth of microorganisms in an application will vary. Typically, the amount of the composition of the present invention is sufficient to control the growth of microorganisms if it provides from 50 to 700 ppm (parts per million) active ingredients of the composition. It is preferred that the active ingredients (i.e., nonionic surfactant and MIT) of the composition be present in the medium to be treated in an amount of at least 70 ppm, preferably at least 90 ppm, preferably at least 110 ppm, preferably at least 120 ppm, preferably at least 130 ppm, preferably at least 140 ppm. It is preferred that the active ingredients of the composition be present in the locus in an amount of no more than 600 ppm, preferably no more than 550 ppm, preferably no more than 500 ppm, preferably no more than 450 ppm, preferably no more than 400 ppm, preferably no more than 350 ppm. In a method of this invention, a composition is treated to inhibit microbial growth by adding, together or separately, the nonionic surfactant and MIT, in amounts that would produce the concentrations indicated above.

Examples

Surfactants and biocides were evaluated for synergy by determining the synergy index (S.I.) of the combination. Synergy index was calculated based on minimum inhibitory concentrations (MIC) of two antimicrobial compounds (A and B) alone and in combinations. The tests organisms were Gram negative bacteria (Pseudomonas aeruginosa ATCC #15442), Gram positive bacteria (Staphylococcus aureus ATCC #6538), yeast (Candida albicans ATCC #10203) and mold (Aspergillus niger ATCC#16404). Contact time for the bacteria was 24 and 48 hours, yeast was 48 and 72 hrs, and 3 and 7 days for mold. The test was carried out in 96 well microtiter plates.

Surf. A R¹O(CH₂CH(CH₃)O)₅(CH₂CH₂O)₉H, where R¹ is 2-ethylhexyl Surf. D R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₅H Surf. E R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H In Surf. D and Surf. E, R² is a mixture of C₈-C₁₄ linear alkyl groups (70% C₈-C₁₀ linear alkyl and 30% C₁₂-C₁₄ linear alkyl)

Inoculums Used

Inoculum Size of organisms (CFU/ml) Aspergillus Candida Staphylococcus Pseudomonas niger albicans Surfac- aureus aeruginosa ATCC# ATCC# tants ATCC# 6538 ATCC # 15442 16404 10203 Surf. A 1.156E+06 8.134E+07 1.156E+06 1.156+06 Surf. D 1.808E+05 1.156E+08 1.156E+06 5.726E+05 Surf. E 1.808E+06 5.727E+07 5.726E+05 1.808E+06

TABLE 4 Media Used Media Used for testing Staphylococcus Pseudomonas Aspergillus aureus aeruginosa niger Candida albicans ATCC# 6538 ATCC # 15442 ATCC# 16404 ATCC#10203 10% Tryptic soy 10% Tryptic soy Potato dextrose Potato dextrose broth broth broth broth

The pH of the Triptic soy broth was 7.3 and the Potato dextrose broth was 5.1.

The test results for demonstration of synergy of the MIC combinations are shown in the tables below. Each table shows the results for combinations of two components against the microorganisms tested with incubation times; the end-point activity in ppm measured by the MIC for compound A alone (CA), for component B alone (CB), and the mixture (Ca) and (Cb); the calculated SI value; and the range of synergistic ratios for each combination tested. SI is calculated as follows:

Ca/CA+Cb/CB=Synergy Index (“SI”)

Wherein:

-   -   CA=concentration of compound A in ppm, acting alone, which         produced an end point (MIC of Compound A).     -   Ca=concentration of compound A in ppm, in the mixture, which         produced an end point.     -   CB=concentration of compound B in ppm, acting alone, which         produced an end point (MIC of Compound B).     -   Cb=concentration of compound B in ppm, in the mixture, which         produced an end point.         When the sum of Ca/CA and Cb/CB is greater than one, antagonism         is indicated. When the sum is equal to one, additivity is         indicated, and when less than one, synergism is demonstrated.

The ratio ranges at which MIT and the surfactants were tested are as summarized in the following table:

MIT with Surf. A Organism ATCC# From To Ratio Range Staphylococcus 6538 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 aureus Aspergillus 16404 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 niger Candida 10203 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 albicans Pseudomonas 15442 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 aeruginosa

MIT with Surf. E Organism ATCC# From To Ratio Range Staphylococcus 6538 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 aureus Aspergillus 16404 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 niger Candida 10203 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 albicans Pseudomonas 15442 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 aeruginosa

MIT with Surf. D Organism ATCC# From To Ratio Range Staphylococcus 6538 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 aureus Aspergillus 16404 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 niger Candida 10203 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 albicans Pseudomonas 15442 0.2:20,000 1,000:218.75 1:0.00001-1:4.5714 aeruginosa

A: Surf. A B: MIT Media: PDB Inoculum size: 1.156E+06 CFU/ml PPM AI MIC Values (3rd day) Test Alone Combination Ratio Organism CA CB Ca Cb S.I. (Ca:Cb) A. niger >20000 400 20000 300 <1.75 1:0.0150 ATCC#16404 >20000 400 10000 300 <1.25 1:0.0300 >20000 400 5000 300 <1.00 1:0.0600 >20000 400 2500 300 <0.88 1:0.1200 >20000 400 1750 300 <0.84 1:0.1714 >20000 400 875 300 <0.79 1:0.3429 >20000 400 437.5 300 <0.77 1:0.6857 >20000 400 218.75 300 <0.76 1:1.3714 A: Surf. A B: MIT Media: PDB Inoculum size: 1.156E+06 CFU/ml PPM AI MIC Values (48 hrs) Test Alone Combination Organism CA CB Ca Cb S.I. Ratio (Ca:Cb) C. albicans >20000 200 20000 100 <1.50 1:0.0050 ATCC#10203 >20000 200 10000 100 <1.00 1:0.0100 >20000 200 5000 100 <0.75 1:0.0200 >20000 200 2500 100 <0.63 1:0.0400 >20000 200 1750 100 <0.59 1:0.0571 A: Surf. A B: MIT Media: 1/10 TSB Inoculum size: 8.134E+07 CFU/ml PPM AI MIC Values (24 hrs) Test Alone Combination Organism CA CB Ca Cb S.I. Ratio (Ca:Cb) Ps. aeruginosa >20000 40 20000 30 <1.75 1:0.0015 ATCC#15442 >20000 40 10000 30 <1.25 1:0.0030 >20000 40 5000 30 <1.00 1:0.0060 >20000 40 2500 30 <0.88 1:0.0120 >20000 40 1750 30 <0.84 1:0.0171 >20000 40 875 30 <0.79 1:0.0343 >20000 40 437.5 30 <0.77 1:0.0686 >20000 40 218.75 30 <0.76 1:0.1371 No synergy: S aureus

A: Surf. D B: MIT Media: PDB Inoculum size: 5.726E+05 CFU/ml PPM AI MIC Values (48 hrs) Test Alone Combination Organism CA CB Ca Cb S.I. Ratio (Ca:Cb) C. albicans >20000 200 20000 50 <1.25 1:0.0025 ATCC#10203 >20000 200 10000 50 <0.75 1:0.0050 >20000 200 10000 60 <0.80 1:0.0060 >20000 200 10000 80 <0.90 1:0.0080 >20000 200 10000 100 <1.00 1:0.0100 >20000 200 5000 50 <0.50 1:0.0100 >20000 200 5000 60 <0.55 1:0.0120 >20000 200 5000 80 <0.65 1:0.0160 >20000 200 5000 100 <0.75 1:0.0200 >20000 200 2500 60 <0.43 1:0.0240 >20000 200 2500 80 <0.53 1:0.0320 >20000 200 2500 100 <0.63 1:0.0400 >20000 200 1750 60 <0.39 1:0.0343 >20000 200 1750 80 <0.49 1:0.0457 >20000 200 1750 100 <0.59 1:0.0571 >20000 200 875 80 <0.44 1:0.0914 >20000 200 875 100 <0.54 1:0.1143 A: Surf. D B: MIT Media: 1/10 TSB Inoculum size: 1.16E+08 PPM AI MIC Values (24 hrs) Test Alone Combination Organism CA CB Ca Cb S.I. Ratio (Ca:Cb) Ps. aeruginosa >20000 30 20000 20 <1.67 1:0.0010 ATCC#15442 >20000 30 10000 20 <1.17 1:0.0020 >20000 30 5000 20 <0.92 1:0.0040 >20000 30 2500 20 <0.79 1:0.0080 >20000 30 1750 20 <0.75 1:0.0114 A: Surf. D B: MIT Media: 1/10 TSB Inoculum size: 1.808E+05 PPM AI MIC Values (24 hrs) Test Alone Combination Organism CA CB Ca Cb S.I. Ratio (Ca:Cb) S. aureus >20000 60 20000 2 <1.03 1:0.0001 ATCC# 6538 >20000 60 10000 0.8 <0.51 1:0.0001 >20000 60 10000 10 <0.67 1:0.0010 >20000 60 10000 20 <0.83 1:0.0020 >20000 60 10000 30 <1.00 1:0.0030 >20000 60 5000 0.6 <0.26 1:0.0001 >20000 60 5000 1 <0.27 1:0.0002 >20000 60 5000 10 <0.42 1:0.0020 >20000 60 5000 20 <0.58 1:0.0040 >20000 60 5000 30 <0.75 1:0.0060 >20000 60 5000 40 <0.92 1:0.0080 >20000 60 1750 0.2 <0.09 1:0.0001 >20000 60 875 0.2 <0.05 1:0.0002 >20000 60 875 0.4 <0.05 1:0.0005 >20000 60 875 0.8 <0.06 1:0.0009 >20000 60 875 1 <0.06 1:0.0011 >20000 60 875 10 <0.21 1:0.0114 >20000 60 875 20 <0.38 1:0.0229 >20000 60 875 10 <0.21 1:0.0114 >20000 60 875 30 <0.54 1:0.0343 >20000 60 437.5 0.8 <0.04 1:0.0018 >20000 60 437.5 1 <0.04 1:0.0023 >20000 60 437.5 10 <0.19 1:0.0229 >20000 60 437.5 20 <0.36 1:0.0457 >20000 60 437.5 10 <0.19 1:0.0229 >20000 60 437.5 30 <0.52 1:0.0686 >20000 60 218.75 50 <0.84 1:0.2286 No synergy: A. niger

A: Surf. E B: MIT Media: PDB Inoculum size: 1.156E+06 CFU/ml PPM AI MIC Values (3rd day) Test Alone Combination Ratio Organism CA CB Ca Cb S.I. (Ca:Cb) A. niger >20000 300 20000 200 <1.67 1:0.0100 ATCC#16404 >20000 300 10000 200 <1.17 1:0.0200 >20000 300 5000 200 <0.92 1:0.0400 >20000 300 2500 200 <0.79 1:0.0800 >20000 300 1750 200 <0.75 1:0.1143 >20000 300 875 200 <0.71 1:0.2286 >20000 300 437.5 200 <0.69 1:0.4571 >20000 300 218.75 200 <0.68 1:0.9143 A: Surf. E B: MIT Media: PDB Inoculum size: 1.808E+06 PPM AI MIC Values (48 hrs) Test Alone Combination Ratio Organism CA CB Ca Cb S.I. (Ca:Cb) C. albicans >20000 200 20000 60 <1.30 1:0.0030 ATCC#10203 >20000 200 10000 60 <0.80 1:0.0060 >20000 200 10000 100 <1.00 1:0.0100 >20000 200 5000 60 <0.55 1:0.0120 >20000 200 5000 80 <0.65 1:0.0160 >20000 200 5000 100 <0.75 1:0.0200 >20000 200 2500 60 <0.43 1:0.0240 >20000 200 2500 80 <0.53 1:0.0320 >20000 200 2500 100 <0.63 1:0.0400 >20000 200 1750 80 <0.49 1:0.0457 >20000 200 1750 100 <0.59 1:0.0571 >20000 200 1750 200 <1.09 1:0.1143 >20000 200 875 80 <0.44 1:0.0914 >20000 200 875 100 <0.54 1:0.1143 >20000 200 437.5 80 <0.42 1:0.1829 >20000 200 437.5 100 <0.52 1:0.2286 >20000 200 218.75 100 <0.51 1:0.4571 A: Surf. E B: MIT Media: 1/10 TSB Inoculum size: 1.808E+06 CFU/ml PPM AI MIC Values (24 hrs) Test Alone Combination Organism CA CB Ca Cb S.I. Ratio (Ca:Cb) S. aureus >20000 60 20000 50 <1.83 1:0.0025 ATCC# 6538 >20000 60 10000 40 <1.17 1:0.0040 >20000 60 5000 40 <0.92 1:0.0080 >20000 60 5000 50 <1.08 1:0.0100 >20000 60 2500 40 <0.79 1:0.0160 >20000 60 2500 50 <0.96 1:0.0200 >20000 60 1750 40 <0.75 1:0.0229 >20000 60 1750 50 <0.92 1:0.0286 >20000 60 875 40 <0.71 1:0.0457 >20000 60 875 50 <0.88 1:0.0571 >20000 60 437.5 30 <0.52 1:0.0686 >20000 60 437.5 40 <0.69 1:0.0914 >20000 60 437.5 50 <0.86 1:0.1143 >20000 60 218.75 40 <0.68 1:0.1829 >20000 60 218.75 50 <0.84 1:0.2286 No synergy: P. aeruginosa The following biocides had no synergy against any organism tested when paired with the following surfactants: Surf. A

Sodium Benzoate, TRIS NITRO

Surf. E

DMDMH

Surf. D

CS-1246, OPP, DMDMH

In the following combinations, the ratio of surfactant to biocide where synergy was observed were not commercially relevant, i.e., a ratio of 1:0.2 or greater (less biocide relative to surfactant). At these ratios, the biocide levels in a formulated product would be too low to be practical: Surf. A

DIDAC, IPBC

Surf. E

CMIT/MIT, IPBC, OIT, TTPC, WSCP

Surf. D

CMIT/MIT, OIT, DIDAC

(MBIT, IPBC, WSCP were synergistic only at 1:0.05 or worse except for one data point)

Stability Testing

A solution of MIT in water was made and diluted with surfactant to give the desired ratios of biocide to surfactant. Additional water was added as needed to give the indicate wt % solutions. The samples were split into three vials. One vial was stored at room temperature, one was stored at 40° C. and one was stored at 50° C. Samples were evaluated after a week to determine stability. Samples that were cloudy or highly discolored were determined to be unstable. In the data tables, a dash indicates that the formulation was stable.

Stability Data—25% MIT in combination with Surfactants—Day 1 Note: all samples were slightly yellow from the biocide

Temperature Room Surfactant Surfactant:MIT Temperature 40° C. 50° C. Surf. D 1:1 — — —   1:0.2 — — — Surf. E 1:1 — — — Surf. A 1:1 — — — TERGITOL L-62 1:1 — — — TERGITOL L-81 1:1 Cloudy Cloudy Cloudy TERGITOL L-61 1:1 Cloudy Cloudy Cloudy TERGITOL 15-S-7 1:1 — — — Stability Data—25% MIT in combination with Surfactants—Day 4 Note: all samples were slightly yellow from the biocide

Temperature Room Surfactant Surfactant:MIT Temperature 40° C. 50° C. Surf. D 1:1 — — —   1:0.2 — — — Surf. E 1:1 — — — Surf. A 1:1 — — — TERGITOL L-62 1:1 — — — TERGITOL L-81 1:1 Cloudy Cloudy Cloudy TERGITOL L-61 1:1 Cloudy Cloudy Cloudy TERGITOL 15-S-7 1:1 — — — Stability Data—25% MIT in combination with Surfactants—Day 7 Note: all samples were slightly yellow from the biocide

Temperature Room Surfactant Surfactant:MIT Temperature 40° C. 50° C. Surf. D 1:1 — — —   1:0.2 — — — Surf. E 1:1 — — — Surf. A 1:1 — — — TERGITOL L-62 1:1 — — — TERGITOL L-81 1:1 Cloudy Cloudy Cloudy TERGITOL L-61 1:1 Cloudy Cloudy Cloudy TERGITOL 15-S-7 1:1 — — — 

1. A synergistic microbicidal composition comprising: (a) a nonionic surfactant with structure: R¹O(CH₂CH(CH₃)O)₅(CH₂CH₂O)₉H where R¹ is a C₈ alkyl group; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.005 to 1:1.3714.
 2. The synergistic microbicidal composition of claim 1 in which R¹ is 2-ethylhexyl.
 3. A method for inhibiting the growth of microorganisms in an aqueous medium; said method comprising adding to said aqueous medium: (a) a nonionic surfactant with structure: R¹O(CH₂CH(CH₃)O)₅(CH₂CH₂O)₉H where R¹ is a C₈ alkyl group; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.005 to 1:1.3714.
 4. The method of claim 3 in which R¹ is 2-ethylhexyl.
 5. A synergistic microbicidal composition comprising: (a) a nonionic surfactant with structure: R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.006 to 1:0.9143.
 6. The synergistic microbicidal composition of claim 5 in which said mixture of C₈-C₁₄ linear alkyl groups comprises from 60 to 75 wt % C₈-C₁₀ linear alkyl groups and 25 to 40 wt % C₁₂-C₁₄ linear alkyl groups.
 7. A method for inhibiting the growth of microorganisms in an aqueous medium; said method comprising adding to said aqueous medium: (a) a nonionic surfactant with structure: R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₇H where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.006 to 1:0.9143.
 8. The method of claim 7 in which said mixture of C₈-C₁₄ linear alkyl groups comprises from 60 to 75 wt % C₈-C₁₀ linear alkyl groups and 25 to 40 wt % C₁₂-C₁₄ linear alkyl groups.
 9. A synergistic microbicidal composition comprising: (a) a nonionic surfactant with structure: R²O(CH₂CH(CH₃)O)₃(CH₂CH₂O)₅H where R² is a mixture of C₈-C₁₄ linear alkyl groups; and (b) 2-methyl-4-isothiazolin-3-one; wherein a weight ratio of said nonionic surfactant to 2-methyl-4-isothiazolin-3-one is from 1:0.001 to 1:0.1143.
 10. The synergistic microbicidal composition of claim 9 in which said mixture of C₈-C₁₄ linear alkyl groups comprises from 60 to 75 wt % C₈-C₁₀ linear alkyl groups and 25 to 40 wt % C₁₂-C₁₄ linear alkyl groups. 